Many communication systems are called upon to communicate a large number of messages from an originating station, through a relaying station, to a large number of receiving stations. By way of example, in a wireless communication system, such as a cellular telephone system, a signal containing a large number of messages might be uplinked from a cellular telephone provider to an earth orbiting satellite from which the messages are relayed to respective ground based receiving stations. It is desirable to minimize the equipment required on the relaying station, particularly when it is a satellite. Not only does minimizing the equipment reduce the cost of the satellite itself, but also it reduces the size of the satellite, and so reduces the cost involved in launching the satellite and placing it in the proper earth orbit.
In a hub and spoke multiple spot-beam communication satellite system, a set of N gateways or hubs provides bandwidth to several user ground cells or spokes in a forward direction. In a return direction, a set of user ground cells communicates back to the corresponding gateways. In the forward direction, a signal in a continuous frequency band of bandwidth B may be uplinked from the gateway to the satellite. The satellite demultiplexes the bandwidth into N segments of various bandwidths such that the N frequency bands occupy the full bandwidth B. The satellite then further processes each of the N bands by filtering, amplifying, and downlinking each band to an appropriate user ground cell. Each user ground cell receives a respective one of the N frequency bands.
The satellite filters each band to reduce adjacent channel interference and applies each band to a respective amplifier, for example a traveling wave tube amplifier. As the number of gateways increases so as to increase network capacity, the satellite requires a larger number of traveling wave tubes, resulting in a significant increase in the satellite size and weight, as well as in power consumption. Because satellites have size and power limits, increasing the number of gateways that can be accommodated requires decreasing the size and power requirements of the equipment needed for each gateway.